Superconductivity of lanthanum and cerium at high pressures

A theoretical model involving the presence of an inner 4f shell is developed here to explain the pressure dependence of the superconducting transition temperature of lanthanum and the presence of a superconducting high pressure phase of cerium. In this model, only the conduction electrons are assumed to participate in the superconductivity mechanism, while the 4f electrons tend to inhibit superconductivity. As the 4f character decreases with increasing pressure in lanthanum, it is possible to account for the anomalous pressure dependence of the superconducting transition temperature by assuming a valency a little less than three at normal pressure. The anomalous behaviour of cerium, magnetic at room temperature and normal pressure and superconducting above 50 kbar, is also discussed here.